package com.hbnu.utils;

import org.springframework.stereotype.Component;

@Component
public class SnowFlake {

    /**
     * 数据中心ID
     */
    private long datacenterId;

    /**
     * 机器ID
     */
    private long machineId;

    /**
     * 序列号
     */
    private long sequence = 0L;

    /**
     * 上一次生成ID的时间戳
     */
    private long lastTimestamp = -1L;

    /**
     * 开始时间戳（2010-01-01）
     */
    private final static long START_TIMESTAMP = 1262275200000L;

    /**
     * 每一部分占用的位数
     */
    private final static long SEQUENCE_BIT = 12; //序列号占用的位数
    private final static long MACHINE_BIT = 10;  //机器标识占用的位数
    private final static long DATACENTER_BIT = 2; //数据中心占用的位数

    /**
     * 每一部分的最大值
     */
    private final static long MAX_DATACENTER_NUM = ~(-1L << DATACENTER_BIT);
    private final static long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);
    private final static long MAX_SEQUENCE_NUM = ~(-1L << SEQUENCE_BIT);

    /**
     * 每一部分向左的位移
     */
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTAMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

    public SnowFlake() {
        this.datacenterId = 0;
        this.machineId = 0;
    }

    public SnowFlake(long datacenterId, long machineId) {
        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
            throw new IllegalArgumentException("Datacenter ID can't be greater than " + MAX_DATACENTER_NUM + " or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("Machine ID can't be greater than " + MAX_MACHINE_NUM + " or less than 0");
        }
        this.datacenterId = datacenterId;
        this.machineId = machineId;
    }

    /**
     * 获取最近一次时间戳
     *
     * @return 最近一次时间戳
     */
    private long getNewstmp() {
        return System.currentTimeMillis();
    }

    /**
     * 等待下一毫秒
     *
     * @param lastTimestamp 上次生成ID的时间戳
     * @return 当前时间戳
     */
    private long getNextMill(long lastTimestamp) {
        long timestamp = getNewstmp();
        while (timestamp <= lastTimestamp) {
            timestamp = getNewstmp();
        }
        return timestamp;
    }

    /**
     * 产生下一个ID
     *
     * @return SnowflakeId
     */
    public synchronized long nextId() {
        long timestamp = getNewstmp();
        if (timestamp < lastTimestamp) {
            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
        }
        if (lastTimestamp == timestamp) {
            sequence = (sequence + 1) & MAX_SEQUENCE_NUM;
            if (sequence == 0) {
                timestamp = getNextMill(lastTimestamp);
            }
        } else {
            sequence = 0L;
        }

        lastTimestamp = timestamp;

        return ((timestamp - START_TIMESTAMP) << TIMESTAMP_LEFT)
                | (datacenterId << DATACENTER_LEFT)
                | (machineId << MACHINE_LEFT)
                | sequence;
    }

    public static void main(String[] args) {
        SnowFlake snowFlake = new SnowFlake(1, 1);

        //测试产生雪花ID
        for (int i = 0; i < 10; i++) {
            System.out.println(snowFlake.nextId());
        }
    }
}